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Patent 1159695 Summary

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(12) Patent: (11) CA 1159695
(21) Application Number: 1159695
(54) English Title: PROCESS FOR MANUFACTURING GROUNDWOOD PULP WHILE MAINTAINING A HIGH AND UNIFORM MOISTURE CONTENT IN THE WOOD IN THE GRINDING ZONE
(54) French Title: PROCEDE DE FABRICATION DE PATE MECANIQUE ASSURANT UN DEGRE UNIFORME ET ELEVE D'HUMIDITE DANS LE BOIS AU COURS DU FEFIBRAGE
Status: Term Expired - Post Grant
Bibliographic Data
(51) International Patent Classification (IPC):
  • D21B 1/00 (2006.01)
  • D21B 1/18 (2006.01)
(72) Inventors :
  • LINDAHL, JONAS A. I. (Sweden)
  • JOHNSSON, GUSTAF E. (Sweden)
(73) Owners :
  • MO OCH DOMSJO AKTIEBOLAG
(71) Applicants :
(74) Agent: MACRAE & CO.
(74) Associate agent:
(45) Issued: 1984-01-03
(22) Filed Date: 1981-06-29
Availability of licence: N/A
Dedicated to the Public: N/A
(25) Language of filing: English

Patent Cooperation Treaty (PCT): No

(30) Application Priority Data:
Application No. Country/Territory Date
80 05035-4 (Sweden) 1980-07-09

Abstracts

English Abstract


16-253
Case 1421
PROCESS FOR MANUFACTURING GROUNDWOOD PULP WHILE
MAINTAINING A HIGH AND UNIFORM MOISTURE CONTENT IN
THE WOOD IN THE GRINDING ZONE
ABSTRACT OF THE DISCLOSURE
A process is provided for manufacturing groundwood pulp
of uniform quality by maintaining a high and uniform moisture content
in the wood in the grinding zone which comprises grinding debarked
wood logs or wood chips in a closed pocket grinder under atmospheric
or superatmospheric pressure while applying shower water both to
the free surfaces of the grindstone and to the grinding zone where the
logs or chips are in contact with the grindstone, such as by spraying
the water at the end portions of the logs or chip mass, optionally
together with applying shower water via the ram plates and a water
trap arranged around the lower part of the log pockets, and prefer-
ably retaining shower water within the grinding zone by filling with
shower water the hollows between the logs or chips located nearest
the surface of the grindstone.


Claims

Note: Claims are shown in the official language in which they were submitted.


THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A process for manufacturing groundwood pulp of uniform
quality by maintaining a high and uniform moisture content in the wood
in the grinding zone, which comprises grinding wood by thrusting the
wood contained in at least one pocket against the surface of a rotating
grindstone in a pocket grinder while applying shower water both onto
the free surfaces of the grindstone at an acute angle and directly into
the grinding zone area where the wood in each pocket and the grindstone
are in surface contact with each other and to portions of the wood charge
spaced from and located immediately above the surface of the grindstone
in a sufficient amount to prevent drying of the wood in the course of the
frictional heating resulting from its being thrust against the surface of the
grindstone, and thus holding the moisture content of the wood at a high
and uniform level.
2. A process according to claim 1 in which the wood is in the
form of logs and which comprises applying shower water to at least one
end portion of the logs and along a line of trajectory that is substantially
in alignment with the longitudinal axis of the logs and at an angle within the
range from about 0 to about 60° to a line parallel to that axis.
3. A process according to claim 2, which comprises maintaining
hollows between adjacent logs in each pocket filled with shower water.

4. A process according to claim 3 which comprises
providing a water trap at the lowermost part of each pocket.
5. A process according to claim 4, in which the water trap
comprises elements located at the two plane ends of the grindstone,
and other elements connected with the end and side plates arranged
around each pocket, in a manner such as to hold the shower water
within the hollows between the logs in each pocket.
6. A process according to claim 2 in which the shower
water is introduced into the grinding zone via spray pipes and through
holes made in said pipes.
7. A process according to claim 2 in which the shower
water is introduced into the grinding zone via spray pipes and through
nozzles mounted on the pipes.
8. A process according to claim 7 in which in addition to
supplying shower water via spray pipes, the shower water is also
applied to the logs from above through openings or nozzles arranged
in each ram plate of each pocket.
9. A process according to claim 1 in which the shower
water is maintained at a superatmospheric pressure within a range
from about 0. 5 to about 40 kp/cm2 above atmospheric.
10. A process according to claim 1 in which the total flow
of shower water is so controlled that the total volume of water intro-
duced directly into the grinding zone is within the range from about 50
to about 600 liters/minute, for each ton of pulp produced per hour.
21

11. A process according to claim 10 in which the total amount
of shower water supplied per ton of pulp per hour is within the range
from about 100 to about 2000 liters/minute, including the shower
water supplied to the free surfaces of the grindstone.
12. A process according to claim 1 in which the shower water
is filtered before application to the grindstone and wood.
13. A process according to claim 1 in which the temperature
of the shower water is within the range from about 65 to about 120°C.
14. A process according to claim 1 in which the temperature
of the shower water is within the range from about 80 to about 105°C.
22

Description

Note: Descriptions are shown in the official language in which they were submitted.


9 ~ 9 5
`
SPECIFICATION
Groundwood pulp is normally produced from debarked logs.
` ~ b,
AccordingtoU.S. patentNo. 4,247,363, patentedJanuary2~, 1981,
to Soma et al, it is also possible to produce groundwood pulp from
5 wood chips. The wood material is thrust against a rotating grindstone
where the abrasive action loosens and releases the wood fibers in the
surface of the wood against the grindstone in a grinding mill, which
may operate at atmospheric pressure or at superatmospheric pressure.
The process generates heat, and the wood fibers tend to ætick
10 to the grindstone, so during grinding of the logs the grindstone surface
is cooled and cleaned by spraying shower water onto the surface. This ~
s~ower water ma~ optionally contain bleaching chemicals. The shower
water normally is al?plied directly onto the free surfaces of the grind-
stone, in the direction of rotation of the grindstone alld/or in the
- . .
15 opposite direction thereto~ at an angle of about 90~ to ~he suspension
and drive shaft of the grindstone. Since the logs l~rought into contact
with the grinding surface lie parallel to the shaft of the stone, the
sho~7er water is applied at an angle o~ about 90 to the long a~is
of the logs.
The fibers freed from the logs durirlg the grinding operation
are collected together with shower water Ul the bottom pit or dam
~; of the grinding mill. The pUl~? concentration in the resultant groundwood
pulp suspension is normally between 0. 5 and 2~c calculated as bone
dry pulp.
, ~ .
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` J 159~95
Wh~n groundwood pulp is ground using stone grinders, the
wood is dried localIy by the frictional heat generated by contact of
the wood with the grinding surface of the stoneO If the wood has a
low moisture content, the wood may even become overheated, and
5 subjected to thermal degradation. As the moisture content of the
wood decreases, the temperature at which the lignin ~ftens
increases,which results in a pulp having rel~tively short fibers. ~uch
~pulps when used for paper manufacture give a paper having, among
other things, a low tear strength. The magnitude of these e~fects
~0 and therefore the quality of the resultant groundwood pulp ~aries
with the moisture content of the wood.
Moreover, the grinding of wood having a low moisture
content can give such a high temperature at-the grinding surface (the
area in which wood and grindstone are in surface contact with each other)
15 that the fibers become discolored, which results in a pulp OI low
brightness, and, furthermore, in a high consumption of chemicals
in any subsequent bleachmg
Thus, in the grinding of wood while spraying shower water
tangentially to the grindstone7 it is ~ifficult to obtain a strong and
20 lig~ pulp of uniform quality, because it is difficult to obtain wood
~tarting materials having a high and unUorm moisture co~tent.
Theæe di~ficulties are resolved by the process of the present
invention, which relates to a method for manufacturing groundwood
pulp from lignocellulosic material, in which wood logs debarked in
25 a known manner or wood chilps are ground in a closed pocket grinderat
atmospheric pressure or at a superatmospheric pressure by spraying

1 15g~95
.. shower water onto the free surfaces of the grindstone at an acute angle,
and, in addition, applying shower water to the grindstone within the
area where the wood and the grindstone are in surface contact with
each other, i. e., to the grinding surface, and to portions of the wood
5 charge located immediately above the surface of the grindstone7
preferably at an angle within the range from about 0 to about 60.
These are collectively referred to herein as the "grinding zone". A
"pocket grinder" is a grinder in which the wood is pressed against the
` ~ grindstone from radially arranged wood pockets.
; ~ 10 This method of applying shower water to the grinding zone oi
the logs or chips has surprisingly been found to prevent undesirable
~ drying of the wood in the course o the frictional heating resulting from
: ~ its being thrust against the surface of the grindstone, and thus holds the
moisture content of the wood at any desired high and uniform level.
. ~ 15 It has been found particularly advantageous to introduce the
shower water to one end portîon or to both end portions of the logs,
~; and to direct the shower water in substantially parallel alignment with
the longitudinal axis of the logs and a~ an angle within the range from
about 0 to about 60. In thls wa~ the hollows between adjacent lQgs
20 are also filled with shower water9 which actively contributes to
. maintaining a high a~d uniform level of moisture in the wood in the
- grinding zone.
;~ When introducing the shower water to the end portions of
~- the logs or to wood chips, it has also been found particularly suitable
,, .

- 1 ~5~95
to arrange a water trap at the lowermost part of each wood pocket.
Such a water trap may suitably comprise plates or like elements
located at the two plane ends and sides of the grindstone, and other
plates connected with the plane ends and side plates arranged around
5 each wood pocket, in a manner such as to hold the shower water
within the grinding zone of the logs or chips to the greatest possible
extent, and thereby making it possible to fill with water into the
.
hollows located between the logs or chips situated nearest the sur- ¦
face of the grindstone at each stage of a grulding operation.
10The shower water is suitably introduced into the grinding
zone of the logs or chips via spray pipes arld through holes made in
said pipes or through nozzles fixedly mounted on the pipes, it having
been found that the shower wa~er should be n~aintained at a super- ¦
atmospheric pressure within the ra~ge from about 0. 5 to about
15 40 kp/cm2, preferably frvm about 5 to about 30 kp/cm2. The shower
:: water pipes, together with the a~orementioned holes or no~zles7 can
be fixedly mounted on the grinder or can be arranged for oscUlatory
movement. The showe~ water can be applied continuously or inter-
mittently at intervals of from five to ten seconds. The spa~ing
20 between the peripheral surface of the grindstone and the nearest spray
delivery point above that surface should be greater than 10 mm.
When it is said that the shower water is applied "substaIltially
in parallel with the longitudinal axis of the logs or chip mass" it is
mea~t that the central portion of the spray projected straight out of
,

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: 1 ~59~g~
..,` ~ .
the holes or nozzles stril~es the surfa~es of the logs or chips at an
angle within the ra~ge flom about 0 to about 60, preferably between
O and 15, to the longitudinal axis of the logs or chip mass.
In addition to supplying shower water via spray pipes the
5 shower water can also be applied to the logs or chips from above
through openlngs or nozzles arranged in each ram plate. This
actively contributes to filling the hollows between the lowermost
adja~e~t logs or chips located nearest the surface of th0 grindstone,
d assists in maintaining a desired high and uniform level of
10 moisture in the wood in the grinding zone.
- ~ The flow of shower water to the logs or chips from all
sources is suitably so controlled that the water introduced direc$1y into
the grinding zone is at a rate within the range from abollt 50 to about
600 liters/minute, for each ton of pulp produced per hour. Totally,
15 thus, the rate of application of shower water per ton of pulp per hour
may vary between 100 and 2000 liters/minute (including the shower
water applied to the free surfaces of the grindstone).
~- It has been f~und of particular advantage to use fLltered
showç~!r water, by filtering the shower water through suitable means
,
; ~ 20 such as a curved æcreen, a drum filter, a centrifuge, or a special
filter. Thus9 for example, shower w~ter which has been ultrafUtered
- ~ can be used to particular advan~ageO
The temperature oP the shower water introduced to the
grinding zone sh~uld be within the range from about 65 to about 120C,
" "~".,~5 ~

l 159~9~ -
preferably from 80 to 105C, this latter xange having been found
particularly advantageous.
The method of applying shower water in accordance with the
invention makes it possible to produce groundwood pulp which is
5 stronger and brighter and of more uniform quality than groundwood
pulp produced in accordaxlce with the conventional shower water
application methods. A further importallt adv~ntage is that high
quality groundwood is produced from aged wood, which has been
stored, and has a low moisture content. During the method of the
10 invention drying of the wood during the grinding process is substan-
tially entirely prevented, thereby greatly decreasing the risk of
harmful overheating. This al~ greatly increases the useful life span
of the grindstone, and above all reduces the risk of damage to the
grindstone, which is of significant i~nportance, since a damaged grind-
`.: !
15 stone normally results in a drop in production with associated economiclosses. ~nother advantage is that the pulp produced is brighter, due
to the fact that the fibers axe not discolored by local overheating in
the grinding zone.
A further ~dvantage aforded by the invention is that the flow
20 o~ shower water can be distributed within the grinder more uniformly
which ma~es it possible to reduce the total amount of shower water
required. This reduction in the flow of shower water results in a
higher pulp consistency in the resultant groundwood pulp suspension.
ThLs is of particular advalltage when the pulp is to be stored in a tower
,
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~ ~59~95
subsequent to leaving the grinder, since the tower can then be made
relatively smaller.
A further advantage afforded by a higher pulp consistency
Is that it is cheaper to dewater the pulp suspension prior to drying,
5 as well as prior to any subsequent bleaching stage. If subsequent
bleaching of the pulp is desired, bleaching can be effected to advantage
in accordance with ~e method described in U . ~. patent No. 4,160, 693,
patented July 10, l9q9, to Lindahl et al.
Grolxndwood pulp produced iIl accordance with the invention
10 has a high content of long and fle2~ible fibers, which produce a strong
paper. Alternatively, this property can be utilized ill the manufacture
of paper having a lower grammage than no~mal whUe retaining good
mechallical strength properties. Further, when mix~d with chemical
pulp, such as sulphate pulp, or sulphite pulp, the pulp manufactured
15 in accordance with the invention can be utilized in grea~er qu~tities
than normal, thereby reducing the cost of ma~ufa~turing paper. The
groundwood pulp is also suitable for the manufactllre of paper of a
wider alld more varying quality range than is normal for pulps with a
yield within the raTlge from 92 to 98%. This is due to the high degree
20 of brigh~ness of the re~ult~t pulp, and its high percentage of long
fibers.
Figures 1 to 3 illustrate schematically the conventional wa~er
sprayi~g technique in the grinding of wood to produce groundwood pulp,
~` a~d also the method according to the inYention.
:
.

: i ~L5~9~
Fi~ure 1 is a cr~ss-sectional view of a grindstone which Is
sprayed with shower water in the conventional way, with the shower
water directed at an acute angle onto the free surfaces ~ and B of the
: grindstone from four locations;
. 5 Figure 2 is a top plan view of a grindstone similar to that
shown in Figure 1, where in addition to directing shower water directly
onto the free surfaces of the grindstone, shower water is also supplied
in accordance wîth the present invention; and
Figure 3 is a schematic cross-sectional view of a grinder
.. ,
- 10 in which shower water is supplied .in accordance ~vith the present
invention, with the coll~entional supply of shower water onto ~he
free surfaces of the grindstone omitted, in order to illustrate more
clearly the method according to the invention.
In the system illustrated in Figure 1, debarked logs 1 havîng
15 a moisture content of between 20 and 65~C are pressed heavily against
the grinding stone 3 by means of rams 2, at a ram pressure of fro~
4 to 40 kp/cm2~
The grinder is enclosed and atmospheric pressure or a
superatmo~pheric pressure up to 10 kp/c~n2 above atmospheric is
- 20 normally maintained. During the grindingoperation, shower water
is supplied via pipes 4, 5, 6 and q, and is applied to the free cylindrical
:~. surfaces ~, B of the grindstone at acute angles, but at right angles to
the ~u~pension and driveshaft 8 of the grindstone
! ~.
~ 8
... .

" l 159~9~
In the preferred embodiment of the invention shown in
Figures 2 and 3, shower w~er is also sprayed onto both ends 9, 10
of the logs from spray pipes 11, 12 having nozzle-equipped spray
headers 13 and 14 (see Figure 3). The shower water is directed
5 substantially in parallel with the longitudinal axis of the logs, i; e.,
at an angle of 0, but can be applied to an angle up to 60, and
preferably not exceeding 15.
The shower water sprayed onto the free cylindrical surfaces
A, B of the grinding stone normally is at a superatmosl?heric pressure
10 within the range from about 0. 5 to about 30 kp/cm2 above atmos-
pheric, while the shower water introduced to the grinding zone is at
a superatmospheric pressure within the range from about 0. 5 to
about 40 kp/cm2 above atmospheric, prePerably between 5 a~d 30 kp/cm2
above atmospheric pressure.
The process of the invention is applicable to any kind of wood.
In general, softwood such as spruce and pine can be ground more
easUy than hardwood such as beech and oak, b~lt both types of wood
can be ground satisfactorily using this process. Exemplary hard-
- woods which çan be ground ulclude birch, beech, poplar, eherry,
20 sycamore, hickory, ash, oak, chestnut7 aspen, maple, alder and
eucalyptus. Exernplary softwoods include spruce, fir, pine, cedar,
juniper ~d hemlock.
The wood call be in the form of logs, or large piece~, or
even in small form, such as wood chips having dimensions that are
conventionally employed in pulping processes. Wood slivers and
~ . '

~ ~9~95
spli~ters, wood gra~ules and wood chunks, and other types of wood
fragments can also be used.
The gr~undwood pulp that is obtained in accordance with the
process of the invention can easily be bleached in accordance with
5 known methods by treatment with chlorine, chlorine dioxide, chlorite,
. hypochlorite, pero~ide, peracetate, oxygen or a~ combinations of
these bleaching agents in one or more bleaching sequences as
describedin, forexample, U.S. patentNo. 4,160,393, patented
July 10, 1979 to Lindahl, particularly column 3, lin~es 32 to 48,
: 10 inclusive.
Preferred embodimen:ts of the invention are illustrated in
the following working Examples, in conjunction with controls carried
out in accordance with the conventional spraying technique.
.' ~
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,
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6 ~ ~
- Example 1
This Example illustrates the m,anufacture of un~leached
groundwood pulp from debarked spruce logs, the method according
to the invention being compared with a Control using the co~ventional
method of applying shower water solely to the free sur~aces of the
` 5 grindstone (Control 1).
In the E:xample accordLng to the invention, shower water
in addition was introduced to the grinding æone by spraying at the ends
of the logs. This was done by fittulg one of nine pocket grinders in a
groundwood pulping plant with spray pipes ~upply~ng shower water
at right angles to the end portions of the logs, in accordance with the
;~ method illustrated in F gures 2 and 3O
Debarked spruce logs having an average moisture content 2
of 53~c were charged to the grinder. The logs were pressed against
the sur~ace of the grindstone at a pressure oî 9 kp/cm2. At this ram
15 - pressure, the mean power of the motor driving the grindstone was
found to be 1950 kW The logs were ground at atmospheric pressure,
but the grinder was well sealed, to prevent the loss-of water vapor
formed by friction of the wood ag~inst the grindstone. The groundwood
` ~ pulp suspension obt~ined was discharged from the grinder through a
20 cl~sedc~nduit A suctionfan was connected to the condllit~ir
~- order to recover water vapor and other ga,~es The fan conveyed
the hot vapors to a heat e2~changer in which air was heated from a
~empera~ure of about + 5C to about 40C. Thi, preheated air wa~ ¦
used for f~sh~rying of the groundwood pulp.
11- ``
j !
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"~ ~
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.,
,

- Tn the Example according to the invention, the temperature
~f the shower water was 80C. Shower water was applied to the free
surfaces OI the grindstone at a rate of 800 l/minute under a super-
atmospheric pressure of 9 kp/cm2 above atmospheric. Sllower water
5 was applied to the ends of the logs in the grinding zone at a super-
atmo~spheric pressure of 12 kp/cm2 above atmospheric and a rate of
300 l/min~te. Thus, the total amo~mt of shower water supplied was
1100 l/minute. Samples of the resulting groundwood pulp suspension
ta~en from the closed conduit had a pulp consistency of 2. 72~c. These
10 pulp samples were screened in a laboratory screen having a slot width
of 0.15 mm, before being formed into sheets which were tested for -
paper properties. The average results from five samples are S}lOWIl
in Table I. In addition to pulp and paper properties, the Table also
shows the energy consumed.
15 Control 1
The same gri~der as that used in Example 1 was used
in this test, but with the supply of shower water to ~e pipes 11 and
12, Figures 2 and 3 stopped. Thus, inthis case shower water
was supplied only to the free surfaces of the grindstone. Shower
20 water was applied at a rate of 1600 liters per minute aIld the discharge
pressure was 9 kp/cm2 ~bove atmospheric. Samples of the resulting
;- groundwood pulp suspensio~ taken from the closed c~nduit had a pulp
consistency of 1. 87%. The pulp was treated in the same manner as
~!
l;hat recited in Example 1, and the results are set forth in Table I.
12
.
,. . .
,,

9~9~
.
` . Table I
Control 1 Example 1
Energy consumed when
grinding, kWh/ton 10~5 1085
Canadian Standard Freeness, ml 145 150
Long fiber content according to
Bauer McNett (~ 30 mesh)~c - 15 24
Tensile i~dex7 Nm/g 33 41
Tear indèx, mNm2/g 3~ 6 5.1
Density, kg/m3 382 370
Brightness according to SC~ c 61 63
As seen from the Table, the pulp produced in accardance
d
with the invel*ion (Egample 1) has a surprisingly high content of
long fibers. The long-fiber content o the pulp produced in accord-
~` 15 ance with the invention is 60~C greater than that oi conventional
groundwood pulp (Control 1~. Xt is particul~rly surprising that
pulp produced in accordance with the invention has a substantially
higher tear index. This increase in tear inde2~ is probably due to the -
. high percentage of long fibers. It is also very surprising that the
2û pulp produced according to the i~ ention has such a higil brightnes~.
The reason for this may be that in the method according to the
invention the te~nperature in the grinding zone is ~omew~at lower
due to the more effective supply of cooling shower water to the
: log~ a~ they are ground against the hot ~urface of the grindstone.
. . .
', ' .
; 13
,., ~
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~ ~ ~9~;9~;
Example 2
This Example illustrates the manufacture of groundwood
pulp frorn spruce logs in accordance with the invention, with the
addition of shower water containing bleaching waste liquor from a
5 peroxide bleaching step By ~Ivay of comparison, ground~ood pulp
was also produced in accordance with the conventional technique
with the addition of shower water, using water containing bleaching
waste liquor (Control 2~, as described in UOS. Patent No. 4, 029, 543.
In the tests, the same grinder and grinding conditions
10 were used as in Example 1, with the follo~ing differencesO
In the Example according to the in~ention, the temperature
of the shower water was 85C. This shower water with its content
of bleaching waste liquor had the following compoeition:
Hydrogen peroxide 0.53 g/l
Na2SiO3 (water glass) 2.12 g/l
Diethylenetriaminepentaacetic acid (DTPA) 0~ 08 g/l
Acetic acid 0.94 g/l
Resinand fattyacids 0.13 g/l
Measured pH 8. 4
~; 20 Shower water wa~ applied to the grindstone at a super-
atmosphe ric preæsure of 10 kp/cm2 a~ove atmospheric and a rate
of 900 liters/minute. ~hower water was applied to the ends of the
- logs at a superatmosph0ric pressure of 12 kp/cm2 abo~Te atmospheric,
and a rate of 200 liters/minute. Thus the total volume of shower water
25 supplied in this Example was 1100 liters/minute. S~mples of
the resulting groundwood pulp suspension taken from the closed conduit
f had a pulp consistency of 2. 85~c (average value of five samples). The
,:
14
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l 15~9~
pulp samples ~re screened in a laboratory screen having a slot width
of 0.15 mm, after which hand-made sheets were produced and tested
for paper properties. The results of the analysis and the energy
consumed are set forth in Table II.
5 Control 2
..... I
The same grinder as in Example 2 was used, but with the
supply c~f shower water to the pipes 11 and 12 (Figures 2 and 3) stopped.
Thus, in this case only the free sur~aces of the grindstone were
sprayed with shower water containing bleaching waste liquor. The
~; 10 shower water was charged at a rate of 1700 liters/minute, under a
discharge pressure of 10 kp/cm2 above atmospheric. The shower
water had a temperature o~ 70C. Samples of the resulting groundwood
pulp suspension taken from the closecl conduit had a pulp consistency ¦ -
o~ 1. 65~c. The pulp was treated in the same manner as that recited
15 in Example 2. The results are set forth in Table II.
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598~5
Table II
Control 2 Example 2
Ener~y consumed when grinding,
k~th/ton 1025 1025
Canadian Standard Freeness, ml185 175
Long-fiber content according to
Bauer McNett (~30 mesh), ~c 17 27
Tensile inde~, Nm/g 38 43
Tear index, mNrn2/g 3.9 5.4
~0 Density, kg/m3 362 350
Brightness according to SCAN, ~c 68 72
As seen from the Table, the pulp produced in accordance
with the invention (Example 2) has a very high brightness. Apparently
a more effective bleaching is obtained with the aid of bleaching
15 waste liquor, when the shower water is also supplied directly to the
` grinding zo~e. It may also be that the shower water supplied to
~,!,, the free surfaces of the grindstone has difficulty in penetratmg between
wood and grindstone in the grinding zone. Thus, the high brightness
may have resulted from a slightly lower temperature in the grinding
20 zone, and/or a more abundant supply of residual bleaching shemicals,
.. ; .
originating from l:he bleachiIlg waste liquor.
A significant advantage aPforded by the pre~ent inv~ntion is
that the pulp suspension from the grinder has a relatively high pulp
~ ~ consistency. IP the pulp is to be bleached further, it is possible to
;' ~ 25 ` directly dewater the pulp further to a higher pulp consistency with
!,'~ .,,
the aid of a relatively simple dewatering apparatus. In order to
avoid a htgh fiber c~ter~ in the white water when grinding in the
conventionll way, it is neeessary~because of its lo~v pulp consistency,
16
,.~
.;;' .

~ ~ 159~9~
to first thicken the pulp æuspension on a filter, which is i~pace-
consuming, and requires a high investment cost.
Example 3
This Example illustrates the manufacture of groundwood
5 pulp from spruce logs having a low moisture content. The shower
water used contained bleaching waste liquor. The electrical
power input required during the grinding operation was measured
to be 2000 kW. Groundwood pulp was ~lso produced in the same
grinder in accordance with the conventional method (Control 3) and
with the same electrical power input. I
The Example according to the inventil~n was carried out in
the following manner. Debarked spruce logs having an average
moisture content of 35~c were ground while supplying shower water
containing the same cllemical compounds as in Example 2 and Control 2.
Shower water was applied to the free surfaces of the grindstone at -
a rate of 950 liters/minute under a superatmospheric pressure of
8 kp/cm2 abo~e atmospheric. Shower water was applied to the end
portions of the logs at a rate of 100 liters/minute and a superatmospheric
pressure of 10 kp/cm2 above atmospheric. The temperature of the
20 shower water was 90C.
` - Pulp samples were taken from the closed conduit and
screened in a laboratoxy ~creen having a slot width OI 0.15 mm, prior
to forming sheets and testing îor paper properties. The results
obtained from the tests and the amount of ener~ consumed are
25 set forth in Table IlIo
:,. lq
' .
: ~

l 15~9~
Control 3
.
In this Control, the same grinder ~vas used as in E~ample 3,
with the same electrical power input. Spruce logs having the same
molsture content were used. The supply of shower water to the
pipes 11 alld 12 (Figures 2 and 3) was stopped. Thus, shower ~ater
was applied solely to the free surPaces of the grindstone as con-
ventional. Shower wa~er was charged at a rate of 1800 liters/minute
under a discharge pressure of 8 kp/cm2. The temperature of the
shower water was 70~ .
Pulp samples were taken from the closed ;~onduit and
treated in the same manner as the samples obtainëd from Ega~nple 3.
The resul~s are shown in Table m.
. . .
Table III
Control 3 Example 3
Electrical energy consumed
~, when grinding, k~h/ton 1080 1030
. ~
Canadian Standard Freeness, ml140 170
Long-fiber content according to
Bauer McNet~ (~30 mesh), ~c 9 22
.s, .
'r' ~0 Tensile index, Nm/g 28 40
~, Tear index, mNm2/g 3. 3 4. 8
Brigh~ness according to SCAN, ~c 66 71
.As seen from the Table, the strength values and brightness
... ~ .
of the pulp produced in accordance with the invention are surprisingly
high. This is very surprising in view of the low moisture content
of the wood. It is also seen from the Table that when producing a
, .^
- 18

~ 159~5
- groundwood pulp from wood having a low moisture content, the pulp
obtained is much weaker when the shower water is supplied as in
:; Control 2, solely in accordance with the known technique, i. e.
. directly onto the free surfaces of the grindstone.
Thus, an important ad~antage afforded by the present
method is that groundwood pulp of high and uniform quality can be
prodused, even when the amount oî moisture contained by the wood
varies greatl~.
'
,!
~ , .
t,',`~
;' ' '
~1 ,,
~ .
: 19

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Administrative Status

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Event History

Description Date
Inactive: IPC from MCD 2006-03-11
Inactive: Expired (old Act Patent) latest possible expiry date 2001-01-03
Grant by Issuance 1984-01-03

Abandonment History

There is no abandonment history.

Owners on Record

Note: Records showing the ownership history in alphabetical order.

Current Owners on Record
MO OCH DOMSJO AKTIEBOLAG
Past Owners on Record
GUSTAF E. JOHNSSON
JONAS A. I. LINDAHL
Past Owners that do not appear in the "Owners on Record" listing will appear in other documentation within the application.
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Document
Description 
Date
(yyyy-mm-dd) 
Number of pages   Size of Image (KB) 
Claims 1994-03-02 3 97
Abstract 1994-03-02 1 31
Cover Page 1994-03-02 1 21
Drawings 1994-03-02 1 34
Descriptions 1994-03-02 19 720